dm: Kconfig: Move CONFIG_SYS_MALLOC_F_LEN to Kconfig

Move this option to Kconfig and update all boards.
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/mx6qsabresd_defconfig b/configs/mx6qsabresd_defconfig
index 67c1b77..09b0190 100644
--- a/configs/mx6qsabresd_defconfig
+++ b/configs/mx6qsabresd_defconfig
@@ -1,3 +1,5 @@
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6sabresd/mx6q_4x_mt41j128.cfg,MX6Q"
 CONFIG_ARM=y
 CONFIG_TARGET_MX6SABRESD=y
+CONFIG_SYS_MALLOC_F=y
+CONFIG_SYS_MALLOC_F_LEN=0x400